A method for imaging the human spine by means of a CT system is known from U.S. Pat. No. 5,946,370. Therein two-dimensional data from CT scout images are combined with three-dimensional information from CT scans using simple modelling of vertebrae. It is often, however, preferred to image the spine of the patient in an upright position. A CT system cannot be used in such a case.
In digital X-ray imaging a composition of an image from sub-images is generally used to form a composite image of an elongate scene which is too long to be reproduced in one operation. In medical X-ray diagnostics such a situation occurs notably when an image of the spinal column is made. Using a contemporary digital X-ray examination apparatus it is difficult or even impossible to form an X-ray image of the complete region of the spinal column of the patient to be examined in one exposure. A number of successive X-ray images of portions of the region to be examined are formed, which images together cover the entire region. A method of this kind is also called the translation reconstruction technique and is known from EP 0 655 861 A1. Such a technique can also be used for imaging other parts of the human anatomy.
Due to the complexity of the scene (around the spinal column there are located other portions of the body like the thorax, rib cage, abdomen, head and neck which are also imaged when imaging the spine) and due to the mixture of over-projecting structures, projection images are often of low quality and limit the diagnostic reliability. Even when a normal-curved spine is imaged there are portions of the spine where neighbouring vertebrae may overlap each other in projection images. Furthermore, when the spine of a patient shows an abnormal curvature, e.g. an exagerated forward curvature (lordosis), an exagerated backward curvature (kyphosis) or a lateral curvature (scoliosis), such overlapping structures occur even more in the curved portions of the spine, thus reducing the quality of the projection images further. Another problem arises when the vertebrae of the spine exhibit an axial rotation. Consecutive projection images taken from the same direction will then show axially rotated vertebrae from different angles, thus reducing the diagnostic value of these images.
The translation reconstruction technique gives easy access to digital overview images of a large part of the human anatomy like the spine. Additionally, fluoroscopy can be used for optimum positioning of the patient and the collimators of the X-ray apparatus. However, much of the information contained in this fluoroscopy data currently is not used for the planning and optimizing of the real acquisition of images of the anatomical parts.